二甲四氯钠（MCPA-Na）是我国小麦、水稻、玉米等禾本科作物田中防治阔叶杂草的核心选择性除草剂，其安全性高、成本低、防效稳定，但用量偏差极易引发药害或防效不足。本文严格依据农业农村部《农药登记资料规定》《农药安全使用规范总则》（NY/T 1276–2021）及中国农业科学院植物保护研究所2023年《麦田除草剂科学使用技术手册》等权威文件，聚焦“二甲四氯钠除草剂每亩用多少”这一核心问题，提供可落地、分季节、分区域、全链条的操作方案。
一、权威标准用量：以有效成分（a.i.）为基准，严禁按商品制剂盲目折算
二甲四氯钠原药纯度通常为85%～95%，市售制剂多为13%、20%水剂或56%可溶粉剂。关键原则：用量必须按有效成分（g a.i./亩）计算，而非商品制剂毫升/克数。
根据农业农村部农药检定所《农药登记信息汇总（2024年第1期）》登记数据（登记证号：PD20151238、PD20180456等），以及全国农技中心《2023年冬小麦田杂草防控技术指导意见》（农技植保〔2023〕42号），二甲四氯钠在不同作物上的推荐用量如下：
| 作物 | 施药时期 | 有效成分用量（g a.i./亩） | 对应常见制剂用量（示例） | 来源依据 |
|---|---|---|---|---|
| 冬小麦 | 返青至拔节前（3～5叶期） | 30～45 g a.i./亩 | 20%水剂：150～225 mL/亩；56%可溶粉剂：54～80 g/亩 | 农业农村部农药登记数据库；全国农技中心文件链接 |
| 水稻（移栽田） | 返青后分蘖初期（4～6叶期） | 25～35 g a.i./亩 | 13%水剂：190～270 mL/亩；20%水剂：125～175 mL/亩 | [NY/T 1276–2021《农药安全使用规范 总则》第5.3.2条](http://www.nyinfo.net.cn/standard/detail?id=100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000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